1. Field of the Invention
The present invention generally relates to coding digital video images, and more particularly to reducing loss of image information by automatically adjusting operating parameters utilized in the coding process.
2. Description of Background Art
Digital video systems are becoming increasingly popular, especially in business settings. An example application of a digital video system is a teleconferencing system. Despite their popularity, digital video systems can be extremely expensive in terms of storage and communication costs. The cost of storage and communication is driven by the massive quantity of digital image data which is generated by the system.
One way to reduce costs or improve performance is to reduce the quantity of digital data used to represent images. Various well known compression techniques have been utilized to reduce the quantity of data used to represent a digitized image. While image compression may reduce some of the costs associated with handling digital image data, the downside is that image quality may suffer.
A number of compression techniques conventionally involve linear transformation of the digital image, followed by quantization. and coding of transform coefficients. In this way, the quantized and coded signals may be compressed, transmitted, or stored, and subsequently decompressed using an inverse set of operations.
The Discrete Cosine Transform (DCT) has commonly been used for image compression and decompression. However, because such DCT-based image processing is computationally intensive, various methods have been devised to improve the performance of the transform process.
The DCT process involves computing a set of coefficients to represent the digital image. One approach used to reduce the time required to perform the transform process is to compute only a subset of the coefficients. The selection of the particular subset of coefficients to be computed is based on detected characteristics of the digital image. While yielding acceptable results, the prior art process of classifying a digital image according to its characteristics and then selecting a subset of coefficients has no mechanism to measure the quality of the transformed image. Furthermore, the selection criteria used to classify an image are fixed such that they cannot be easily adjusted to improve image quality.
Therefore, to improve the quality of compressed digital images what is needed is a coding system having self-adjusting selection criteria for selecting a transform function.